It is well-documented that exposure to adult animals to various narcotics produces alterations in the rate at which the hepatic mixed function oxidase system catalyzes the biotransformation of drugs and steroids. Little is known, however, about the effect of perinatal exposure to narcotics on the development of hepatic drug metabolism in neonates, older infants and children. The effects need not be similar to those observed in adults or, if similar, need not be produced by similar dosages. Furthermore, the duration of such an effect on hepatic drug metabolism in the developing child is also unknown. Since a large number of females and males are exposed to drugs of abuse during the reproductive years, the exposure of the pregnant patient and newborn to such drugs represents a significant public health problem. The hazard of this exposure to the unborn child as well as the potential for drug-induced adverse effects during neonatal growth and development are of major concern. The development of a new body of fundamental pharmacologic and toxicologic information applicable to the developing human exposed perinatally to drugs of abuse is necessary if one hopes to establish a rationale basis for the care of this special patient population.